All drugs–nicotine, cocaine, marijuana and others–affect the brain’s “reward” circuit, which is part of the limbic system. This area of the brain affects instinct and mood. Drugs target this system, which causes large amounts of dopamine—a brain chemical that helps regulate emotions and feelings of pleasure—to flood the brain. This flood of dopamine is what causes a “high.” It’s one of the main causes of drug addiction.
Although initial drug use may be voluntary, drugs can alter brain chemistry. This can actually change how the brain performs and interfere with a person’s ability to make choices. It can lead to intense cravings and compulsive drug use. Over time, this behavior can turn into a substance dependency or drug and alcohol addiction.